It is a well-known fact that machines of this type have a base plate or table supporting a model. Disposed right under the moulding box, such plate, driven by a classic hydraulic mechanism, is capable of vertical upward and downward travel so that in the course of the upward displacement it may couple tightly and perfectly to the moulding box and the latter to the frame, whereupon the moulding box and part of the frame are filled with sand that is subsequently compacted through a sudden discharge of blast air. Downward displacement of the base plate releases the coupling and the moulding box can hence be removed with the mould duly structured inside the same and is substituted by another box, for other work to begin.
These machines are moreover provided with a hopper containing sand that, when loading the moulding box with the necessary amount of sand, must be located above the same and afterwards be removed to leave space available for a cup where the blast air to be released collects, such air being discharged into the compacting enclosure when the valve located on the cup's lower base is opened. It is hence clear that there is a synchronized movement to position, depending on the work stage, the hopper or the cup axially to the moulding box. The cup may sometimes be fixed with the hopper as a moving element, or the other way round, in which case the plate or table supporting the moulding box must be moved horizontally, to be positioned under the sand hopper or under the cup, as appropriate.
The cup where the blast air collects, whether fixed or mobile with regard to the moulding box, is in turn provided with a release valve comprising a tilting metal disc, a deformable or other diaphragm that, when the blast air is discharged, opens and allows it to enter the enclosure defined by the moulding box and the frame instantaneously so as to compact the sand inside such enclosure. As aforesaid, when directing the air, deflectors operatively provided to such end in the diffuser may be used.
Once the air has been released and hence the sand has been compacted, air remaining in the compacting enclosure is removed through a delivery valve that should preferably be positioned far from the moulding box to prevent dragging of highly abrasive sand that would damage whatever installation elements it might come across with when going out.
Machines thus formed, among which there are obviously differences depending on the manufacturer, have certain disadvantages, which are put right using the improvements subject hereof.
In fact, one of the most oustanding disadvantages of current machines derives from the use of the cup where the blast air collects to compact the sand, the lower base of such cup being provided with the release valve, and the cup being positioned axially to the moulding box. With this structure and arrangement, the air clearly and naturally tends to be directed, largely and most efficiently, towards the center of the moulding box, resulting in sand moulds with a density that is barely uniform, i.e., very dense in the middle and less so at the sides and ends, although it is particularly beneficial for a good mould density to be obtained peripherally so as to avoid any damage during handling thereof. This disadvantage, derived from the position of the release valve regarding the moulding box, can be overcome to some extent using deflectors partly deviating the blast air towards the peripheral areas of the compacting enclosure, though their efficiency does not wholly solve the problems.
Another typical disadvantage, that has already been mentioned hereinbefore, is that the hopper or the cup must be mobile in order to be placed above the moulding box when loading the same and when releasing the blast air, this requiring the use of mechanisms and means to make such movements possible and that obviously render the machine more complex and costly.
Yet another disadvantage of some sand-box moulding machines currently used is that the sand from the hopper that fills the moulding box and part of the frame is poorly spread out, for no means are provided to level and spread out the sand within the compacting enclosure, such enclosure comprising, as aforesaid, the tightly coupled moulding box and frame.